Some prop guidance for older scarab
 

I have an 84 30' scarab. The boat weighs close to 9000.lbs. The boat has 565 hp 502's with BW and 1.5 TRS. Currently I am turning a 26p 3 blade. The boat runs 73 on gps at 5200 rpm. I would love to only turn the engines 4700-4800 but I would like to see high 70's. I have a datatach prop slip gauge in the boat and at 73 I see a slip of 13-14%. With the 3 blade I do have a problem with the starboard engine blowing out the prop if I bring the engines up at the same rpm so I was thinking a 4 blade will help with this but not sure, any ideas what I should look at for a setup? Is a 30p to big of a jump?

Thanks in advance!
Jim

Why do you want to turn those engines at that low of an rpm???? More than likely you should be spinning them closer to 5500rpms at WOT depending on the cams. Spinning an engine faster is easier on it than lugging it at too low an rpm.

Do you know the cam specs???? or have a dyno sheet????

I doubt you would make even close to 565hp at 4800rpms.

I can tell you that you will not be able to turn 30's . As for running the motor to 5200 that is right on the money. I would try a 26 4 blade to start with. just my .02

my 83 34' Scarab III weighs 7200 empty, I think your 9000 is a littlr high, yes you need to stay around 5200 rpm, I am spinning Hydromotives Q-4's 28" pitch running upper 70's, Dave